The present disclosure relates generally to switching-mode power supplies and control methods thereof, and particularly to power supplies whose product sizes could be very compact.
Power supplies are almost needed for every electronic apparatus, to convert an input power from an electric grid or batteries into an output power specifically demanded by an output load. For example, an output load might be a 25-volt-driven direction-current (DC) motor, and a corresponding power supply should convert the 110V power for grid lines into an output power with steady 25V.
Conversion efficiency is a key issue for most of power supplies. Beside conversion efficiency, contemporary electronic products also concern about product cost and size, in consideration of product competitiveness and portability.
FIG. 1 shows a conventional switching-mode power supply (SMPS) 8 with flyback topology 10. SMPS 8 provides output voltage VOUT at output power node OUT to power output load 20. Controller 18 controls power switch 15 in flyback topology 10, making the transformer energizing or de-energizing. Operation power supplier 12 generates operation voltage VCC at operation power node VCC, to power controller 18.
Even though SMPS 8 is quite welcome in the art, it might induce concerns such as high product cost and size. For example, the transformer in SMPS 8 has three windings, including primary winding PRM, secondary winding SEC and auxiliary winding AUX, whose size and cost in total could be considerable. Furthermore, to regulate output voltage VOUT SMPS 8 commonly employs LT431 (not shown) to compare output voltage VOUT with a target value, and the result is transmitted, via photo coupler (not shown) to compensation node COM of controller 18. Both LT431 and photo coupler cost a lot in view of both space and price.